1. Field Of The Invention
This patent relates to liquid dispensing cartridges for automated dispensing systems. More specifically, this patent relates to an ink cartridge with self-closing valve for use with automatic lithographic presses.
2. Description Of The Related Art
Lithography is a printmaking process dating back to the 1700s in which ink is applied to a plate having both image and non-image areas. The image areas are ink-receptive and water-repellent. The non-image areas are water-receptive and ink-repellent. In rotary type lithographic presses the ink plate is mounted on a cylinder that rotates during printing. In one typical configuration, the plate cylinder picks up the ink at the image areas and transfers the image to a blanket cylinder, which then transfers the image to the paper. In multi-color sheet-fed type lithographic presses, multiple inking stations are placed in series. Each station has its own ink feeding system and handles a separate color. As the paper sheet moves from station to station, a new color is put down at each station.
Because lithographic ink is thixotropic, conventional lithographic ink feeding systems require a complex system of drums, vibrators and fountain rollers to handle and dispense the highly viscous ink. In a typical lithographic ink feeding system, workers remove the ink from a drum (or, in some cases, small tins) with specially made spatulas and spread the ink across a tray (the ink fountain). Fountain rollers roll against the ink fountain to pick up the ink and transfer it to the plate cylinder. The process is labor intensive and subject to error.
It is also difficult to store and reuse lithographic ink in drums. The ink is prone to oxidation which can result in color variations from one press run to another, and even from sheet to sheet within a single run. In addition, upon exposure of the ink to the atmosphere, volatile organic compounds (VOCs) evaporate, which can cause ink spoilage.
Some modern lithographic printers use specially designed cartridges to dispense ink, such as that described in Rea et al. U.S. Pat. No. 6,192,797. These cartridges are much smaller than drums, being typically nine to thirteen inches long and about three and a half to five inches in diameter. During printing, the ink cartridge moves back and forth across the fountain, dispensing ink into a fountain trough or directly onto an ink form roller. In automated presses, the amount of ink in the trough is continually monitored and replenished as needed.
Ink cartridges can be easily filled, transported, used and reused. The cartridge minimizes exposure of the ink to the atmosphere and also minimizes the amount of residual ink left in the cartridge after use.
Ink cartridges typically comprise a hollow cylindrical body, a plunger at one end and a dispensing fitment at the opposite end. The cylindrical body is filled with ink. The plunger can move axially within the cylindrical body. The ink is extruded from the dispenser when the plunger is forced toward the dispensing end by, for example, mechanical or pneumatic pressure.
The dispensing fitment is mounted in sealing engagement within the dispensing end of the cylindrical body and typically has a valve for opening and closing the cartridge. In the ink cartridge described in U.S. Pat. No. 6,192,797, the valve is recessed below the rim of the cartridge so it does not become damaged during shipment and storage. However, the valve must be manually opened to allow ink to flow, which is time consuming and can lead to error. In addition, valves that stay open until manually closed work poorly with lower viscosity inks because of their tendency toxe2x80x9cdrool.xe2x80x9d This is particularly troublesome in the United States, where inks are made with varying degrees of viscosity. A number of automatic valves have been tried that open and close in response to pressure from the ink, but they tend to remain open when the pressure is decreased, thereby allowing ink to continue to be extruded.
Thus there exists a need for an ink cartridge dispensing valve that opens when subjected to pressure from the ink and closes automatically and completely when the pressure is decreased below a certain predetermined level, even when used with lower viscosity inks. The present invention satisfies this need.
The present invention is an improved ink cartridge of the type used to dispense ink in automatic lithographic presses. The ink cartridge comprises a hollow cylindrical body for holding a supply of extrudable ink and has a plunger end and a dispensing end. The plunger end is closed by a plunger adapted to act as a piston within the cylindrical body to extrude the contents of the dispenser when the plunger is forced toward the dispensing end by mechanical or pneumatic pressure. The dispensing end is closed by a dispensing fitment affixed to the cylindrical body by glue or other suitable means. The improvement comprises a valve member mounted over a central aperture in the dispensing fitment, the valve member being adapted to open when subjected to pressure from the ink and close automatically and completely when the pressure is decreased below a certain predetermined level.
In the improved ink cartridge, a substantially cylindrical nozzle extends from the periphery of the dispensing fitment aperture and terminates in a rim. The nozzle defines a substantially cylindrical space. A flexible molded plastic spring is mounted within the cylindrical space and urges the valve member against the nozzle rim. The spring is bowed rearward in the direction of the plunger when the valve member is in the closed position. The spring has openings to accommodate the flow of ink through or around the spring.
The valve member is located downstream of and supported by the spring. The valve member is moveable between a closed position in which the valve member is urged against the nozzle rim by the biasing force of the spring, and an open position in which the valve member is raised above the nozzle rim to create an annular opening when pressure applied by the ink to the spring and to the valve member exceeds the biasing force of the spring.
In one embodiment, the valve member comprises a substantially flat disk-shaped portion and prongs extending upward from the disk-shaped portion and through a hole in the spring to secure the valve member to the spring.
The plunger comprises a substantially circular disk portion and a sidewall extending from the periphery of the disk portion in a direction away from the dispensing fitment. Preferably, the plunger includes an annular ring protruding from the circular disk portion in the direction of the dispensing fitment. The annular ring has a cylindrical outer wall and a concave inner wall and is adapted to fit around the valve member prongs and within the space defined by the nozzle to minimize ink left in the cartridge when the plunger is fully depressed.